Gangliosides are thought to play an important role in many aspects of cellular interaction, and biochemical studies have established quantitative and qualitative changes in ganglioside composition during development and transformation. A study is planned using a subclone recently established in our laboratory of Yaffe's rat skeletal muscle cell line L6, which will terminally differentiate in culture, and a variant of this cell line, D3, which is unable to differentiate and which has been found to be a GM1-negative. Antibody raised in rabbits against the ganglioside GM1 will be used to localize this molecule at the cell surface and goat anti-rabbit IgG coupled with bacteriophage T4 or latex spheres will provide the surface markers for scanning electron microscopy. The proposed study will include the quantitation and topographical distribution of GM1 under a variety of experimental conditions. These will include procedures to enhance or inhibit differentiation as well as transformation with an oncogenic virus.